1. Field of the Invention
The present invention relates to a deformation sensor which is used for detection of automobile crash and so on.
2. Description of the Related Art
Conventionally, as units which measure deformation of components, and a level and distribution of a load acting on target components, piezoelectric sensors using piezoelectric ceramics such as PZT (lead zirconate titanate), and strain gauge type sensors are used. These sensors are expensive, and have the low degree of freedom in shape design. Sensors using piezoelectric polymer such as PVdF (polyvinylidene-fluoride) are proposed. When the piezoelectric polymer is used, a sensor operable temperature range is limited. On the other hand, sensors using pressure sensitive conductive resin are proposed. For example, Japanese Unexamined Patent Publication (KOKAI) No. 9-5014 discloses a bend sensor which measures bending deformation of components based on a change of resistance generated in a pressure sensitive conductive resin film.
Conventional sensors such as piezoelectric sensors detect only local deformation of components. For this reason, it is difficult for the conventional sensors to accurately detect deformation over a wide range of components. The pressure sensitive conductive resin film composing the bend sensor described in Japanese Unexamined Patent Publication (KOKAI) No. 9-5014 is composed of a pressure sensitive conductive ink obtained by blending conductive fillers into polymer. When such a pressure sensitive conductive resin film is pressurized, electric resistance is reduced. That is to say, in non-compressed state, the electric resistance of the pressure sensitive conductive resin film is large, and when compressed, the film is made to be conductive by contact with the conductive fillers in the film, thereby reducing the electric resistance. In the sensor using the pressure sensitive conductive resin film, therefore, when the conductive fillers are brought into a contact state to a certain extent by the compression, a change of the electric resistance becomes small. For this reason, a measuring range is narrow. The sensitivity greatly varies according to the blending percentage of the conductive fillers in the pressure sensitive conductive resin film or the like.